halibut

Etymology

From Middle English *halibutt, equivalent to holy + but (“flatfish”), since the fish was often eaten on holy days. Compare Dutch heilbot, German Heiligbutt, Heilbutt, Heilbutte. Compare also Danish helleflynder, Swedish helgeflundra.

noun

1. A large flatfish of the genus Hippoglossus, which sometimes leaves the ocean floor and swims vertically.
   … she frowned a displeased frown and told me for heaven's sake to stop goggling like a dead halibut. 1960, P. G. Wodehouse, Jeeves in the Offing, chapter IV